Deck 17: Intracellular Messengers

Question 1

The second messenger cyclic adenosine monophosphate (cAMP) induces its effects by binding to the regulatory subunits of protein kinase A.What is the immediate target of the second messenger inositol-1,4,5-trisphosphate (IP₃)?

A)A calcium channel in the endoplasmic reticulum (ER) membrane.
B)Phospholipase C.
C)Protein kinase C.
D)A nuclear DNA-binding protein.
E)Calmodulin.

Answer 1

A calcium channel in the endoplasmic reticulum (ER) membrane.

Question 2

Some hormones act by triggering the release of calcium from the ER.These hormones can regulate gene expression, usually by:

A)The binding of calcium to transcription factors, which in turn bind to promoters and enhancers of genes.
B)The activation of calmodulin-regulated protein kinases that phosphorylate nuclear transcription factors.
C)The direct binding of calcium to the DNA double helix.
D)The methylation of DNA in the promoters and enhancers of genes by a calcium-dependent enzyme.
E)The binding of calcium to mRNA, which stabilizes the RNA against the action of RNA-degrading enzymes.

Answer 2

The activation of calmodulin-regulated protein kinases that phosphorylate nuclear transcription factors.

Question 3

Glucagon can induce gene transcription in the liver.How?

A)It is translocated to the nucleus, where it binds to response elements in the regulatory sequences of the genes.
B)It triggers cAMP formation, and cAMP activates genes by binding to the catabolite activator protein.
C)It releases calcium from the ER, which activates protein kinase C in the nucleus.
D)It causes phosphorylation of nuclear transcription factors by protein kinase A.
E)It induces the formation of the second messenger IP3, which activates transcription by binding to nuclear transcription factors.

Answer 3

It causes phosphorylation of nuclear transcription factors by protein kinase A.

Question 4

You work as research director for a pharmaceutical company.One of your tasks is the development of new antihypertensive (blood pressure-lowering) drugs.The most promising drug would be one that:

A)Inhibits the endothelial nitric oxide synthase.
B)Opens voltage-gated calcium channels in the plasma membrane of vascular smooth muscle cells.
C)Blocks voltage-gated calcium channels in the plasma membrane of endothelial cells but not vascular smooth muscle cells.
D)Inhibits the Gs protein in vascular smooth muscle cells.
E)Prevents the degradation of cAMP in vascular smooth muscle cells but not other cells in the body.

Question 5

The actions of insulin are initiated by:

A)Phosphorylation of the insulin receptor on tyrosine side chains.
B)Stimulation of cAMP synthesis through a G protein.
C)Inhibition of cAMP synthesis through a G protein.
D)Formation of IP3 and diacylglycerol.
E)Activation of a guanylate cyclase.

Question 6

Many cytoplasmic enzymes become activated in response to an elevated calcium concentration.In most cases, these effects are mediated by the protein:

A)Calmodulin.
B)Phospholipase A2.
C)Troponin.
D)Calsequestrin.
E)Calcineurin.

Question 7

A linkage study has found that there is a gene for test-taking skill in a particular region on the long arm of chromosome 4.A search of the human genome sequence shows that this chromosomal region contains a gene of unknown function.This gene encodes a protein that has not only a signal sequence but also seven hydrophobic sequences, each about 20 amino acid residues long.The gene product is most likely:

A)A voltage-gated ion channel.
B)A ligand-gated ion channel.
C)A cytoplasmic protein kinase.
D)A hormone receptor that is linked to G proteins.
E)A hormone receptor with a tyrosine-specific protein kinase activity.

Question 8

One important feature of the insulin receptor is:

A)It phosphorylates proteins on tyrosine side chains.
B)It is coupled to the Gi protein.
C)It is coupled to the Gq protein.
D)It has guanylate cyclase activity.
E)It mediates many of its effects through the production of nitric oxide.

Question 9

IP₃ is a second messenger of many hormones.To form this second messenger, which enzyme is needed?

A)Phosphodiesterase.
B)Protein kinase C.
C)Protein kinase B.
D)Phospholipase C.
E)Ras.

Question 10

cAMP stimulates hormone production and cell proliferation in many endocrine tissues, including the thyroid gland.Therefore, a type of somatic mutation that is most likely to lead to the formation of a hormone-overproducing benign tumor in the thyroid gland (a "toxic nodule") is one that causes:

A)Inability of the Gs protein to hydrolyze its bound guanosine triphosphate (GTP).
B)Inability of the Gi protein to hydrolyze its bound GTP.
C)Inability of the protein kinase A regulatory subunits to respond to cAMP.
D)Absence of the CREB protein.
E)Degeneration of the thyroid-stimulating hormone (TSH)-producing thyrotrophs in the anterior pituitary gland.

Question 11

There is much overlap of the intracellular signaling cascades of growth factors such as epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) with those triggered by:

A)Neurotransmitters.
B)Hormones acting through cyclic guanosine monophosphate (cGMP).
C)Steroid hormones.
D)Insulin.
E)Hormones that are coupled to heterotrimeric G proteins.

Question 12

What is the difference between nicotinic and muscarinic acetylcholine receptors?

A)Nicotinic receptors have guanylate cyclase activity; muscarinic receptors are ion channels.
B)Nicotinic receptors are ion channels; muscarinic receptors are coupled to G proteins.
C)Nicotinic receptors are coupled to G-proteins; muscarinic receptors have adenylate cyclase activity.
D)Nicotinic receptors are coupled to G-proteins; muscarinic receptors are ion channels.
E)Nicotinic receptors are ion channels; muscarinic receptors have tyrosine-specific protein kinase activity.